Diploid & Triploid Rainbow Trout in Idaho
Lakes and Reservoirs
Martin Koenig
Sterile Hatchery Trout - Program Goal
Maintain harvest opportunity while reducing
genetic risks to native trout
….IDFG Sterile fish policy in 2000
Background – sterile trout???
Commercial + Sport fishing
Triploid = 3 sets DNA
Sterile
– no maturation in females
– disrupted maturation in
males
Performance in fisheries??
– Survival
– Growth
– Longevity
Stream Catchables
Sterile Trout
HML Fingerlings
Research
Reservoir fingerlings
Questions remain
…
remain…
Uncertainty remains about 3N performance…
Mainly fingerling studies in lakes
Atypical lakes used for reservoir study
Representative of typical hatchery stocking?
IDFG Resident Hatcheries
$2.3 million dollar
program
Catchable rainbow trout :
$1.2 million (50% !)
About 1.6 million
catchables per year
Over 500 water bodies
stocked
Reservoir catchable evaluation
2N vs. 3N Catchable rainbow
– Growth (length / wt)?
– Longevity?
– Total harvest?
Size ranges: 35 – 482 ha
(Island Park Res = 2,947 ha)
Methods
All-female 2N/3N
Adipose clip + CWT
Reared at Hagerman State
Stocked equal numbers
- Spring 2008
Methods – in the field
Gill nets
– Fall 2008
– Spring 2009
– Fall 2009
Voluntary Creel (“snout boxes”)
– Angler donated snouts
– April to October 2008, 2009
Methods – in the lab
Snouts frozen
CWT dissected
Tag codes via microscope
Results
Total Stocked
2N = 84,523
3N = 85,283
Avg Size at Stocking
2N = 252 mm
3N = 252 mm
Avg Stocking Density
2N = 64.5 fish/ha
3N = 64.2 fish/ha
53%
Bulk of RBT captured are hatchery fish
Carry-over to next season is limited
3N trout had 28% lower return in first year
Mean length (mm)
480
460
Mean Length (mm)
440
438
435
420
400
380
360
340
320
340
321
329
317
300
FALL 2008
SPRING 2009
2N
FALL 2009
3N
No Length advantage of 3N fish
2N fish actually average a little longer (not significant)
Length comparison consistent over time
Mean Weight (g)
1100
1000
Mean weight (g)
900
883
829
800
700
600
500
470
400
357
300
378
328
FALL 2008
SPRING 2009
2N
FALL 2009
3N
No weight advantage of 3N fish at first
2N fish significantly heavier, until second fall
3N catch up in weight by Fall 2009… sexual maturity?
Mean Dressed Weight (g)
1000
Mean Length (mm)
900
800
772
727
700
600
500
406
400
348
300
338
327
FALL 2008
SPRING 2009
2N
FALL 2009
3N
No 3N advantage for dressed weight
Even with removing gonads in 2N fish, still no advantage for
3N fish
Results
2008
Lake Name
Devil Creek Res
Horsethief Res
Island Park Res
Little Camas Res
Lost Valley Res
Mann Lake
Oakley Res
Paddock Res
Roseworth Res
Soldier Meadow Res
Stone Res
Thorn Creek Res
Waha Lake
Grand Total
Gill Nets
3N
2N
33
36
98
118
46
30
85
46
144
94
6
6
5
5
10
1
16
2
35
33
70
27
20
30
57
38
635
456
58%
42%
Voluntary Creel
2N
3N
47
39
442
454
56
28
46
44
66
70
57
55
65
26
5
4
82
44
59
35
81
41
111
89
98
60
1215
989
55%
45%
Gill Nets
2N
3N
3
2
10
18
18
6
0
0
44
45
2
0
0
1
13
11
0
0
62
62
152
145
51%
49%
2009
Voluntary Creel
2N
3N
6
1
11
14
16
14
31
18
2
1
0
0
11
9
13
7
90
64
58%
42%
Differences in 2N v. 3N performance varies across reservoirs
Differences seen in both nets and creel with similar results
What does it mean
…?
mean…?
Idaho reservoirs heavily dependent on hatchery trout
2N seem to have better performance after stocking
– Slightly better length and weight
– Better initial survival and return to creel
Differences in 2N vs. 3N performance variable across
reservoirs
– Water management…?
– Species compositions…?
Similar results from the creel and net data
– Suggests survival differences, not harvest
Now what
…?
what…?
Examine angler-caught tag returns:
– Do catch ratios mimic gill net ratios?
Lake-specific results
– Do ratios change differently across lakes…?
Length / Weight changes next year:
– Sexual maturity/spawning…?
Relative abundance next year:
– Overwinter survival…?
Thanks To:
Joe Chapman - Hagerman Hatchery Staff
Rodney Duke
Brian Leth
Jeff Dillon,
Joe Kozfkay
Steve Elle,
John Walrath,
Brad Wright
Doug Megargle
Dan Garren
Questions?